As we all know, all payment cards have a determined number of digits. Some of those at the front form the “BIN”, which identifies the issuing body of the card, the following digits form the intermediary data, with the exception of the last one, which normally corresponds to the “Check-Digit”. The expiry date is also used as a means of identifying the card.
Whenever the card is used in a commercial operation, in particular over the Internet®, but also when using other networks where specific means of payment are required, the card's true data is exposed to the net, thereby becoming accessible to third persons, and running the perfectly possible, and even frequent, risk of being used at a later date in a fraudulent manner to acquire goods or services, delivering them to a third person, in the name of the cardholder whose specific data is known.
There are various methods that use ciphering, encoding, concealment, etc. of the card number to prevent the payment card's true number from being intercepted.
For example, one of the most important of these is described under European Patent publication number 1 029 311, and is based on a set of valid credit card numbers with one of them being the master, the one that actually works, and at least one more of limited usage, which is connected to the master and which is the number actually sent over communication networks or the Internet®.
This limited usage number is deactivated with a code that can be activated with different aims; for a single transaction, for a limited period of time, for a limited amount of money, etc . . .